As FIG. 1 shows, the conventional practice in assembly technology is currently to connect a machining tool, in particular a hand-operated electrically controllable machining tool such as a single screwdriver or a multiple screwdriver 1 via a connecting rod 2 to a holding unit 3, which is held in a sliding support mechanism 4 such that the holding unit 3 is able to move by sliding in the sliding support mechanism 4. The holding unit 3 is conventionally a travelling box or trolley provided with a number of rollers, which are suspended in a roller rail having a U-shaped profile, for example, which is used as the sliding support mechanism 4.
As the diagrammatic view in FIG. 1 shows, the machining tool 1 naturally needs to be supplied with power, for which purpose a trailing cable installation 31, 32, 33 . . . 3n is used. The cable 5 for the power supply, which is inherently disruptive to the machining process, is typically suspended from cable hanger units 31, 32, 33 . . . 3n, which are likewise held in the roller rail 4. Reference number 6 in FIG. 1 indicates an end fixing device for the cable 5 before it passes to a control unit STE for the machining tool. The trailing cable installation includes not only the power supply lines but also control lines and data lines, as the control unit STE sets the machining tool to predefined machining parameters in order to execute a predefined machining process and in some circumstances feedback also has to be passed from the machining tool 1 to the control unit STE, for example information about the final torque obtained on tightened screws.
Furthermore, the roller rail 4 is not restricted to a purely straight configuration as shown in FIG. 1, of course, but curved designs are also conceivable, such that the machining tool can also move in a curved path along the roller rail 4. Of course, in an assembly line not just one single machining tool, as shown in FIG. 1, is needed; instead, several machining tools 1-1, 1-2 are typically suspended in sections BA1, BA2 in a roller rail 4, as shown in FIG. 2a. Reference number 8 in FIG. 2a indicates a moving belt, WST1, WST2 indicate workpieces, for example vehicles, which move at a preset speed v from one machining zone BA1 to another machining zone BA2, reference numbers 3-1, 3-2 indicate the holding units (trolleys) already shown in FIG. 1 and reference numbers 5-1, 5-2 indicate the cable between the machining tools 1-1, 1-2 and the individual control units ST1, ST2.
As FIG. 2a shows, the entire assembly process is divided into machining sections or machining zones BA1, BA2, whereby each machining tool 1-1, 1-2 can only move along the rail 4 in the machining zone assigned to it. Out-of-range sensors are therefore provided for a minimum warning limit 7-1 and a maximum warning limit 7-2 or 7-4 and 7-3 such that an alarm is issued if the tools leave the zones. It is also possible to provide sensors that cause the production belt 8 to stop in the event of a major range violation. The control units ST1, ST2 can also be jointly controlled from a central processing system ZV, via radio or infrared or via cable, for example.
For example, a door is fitted in a machining zone BA1 in FIG. 2a, such that the control unit ST1 sets the tool 1-1, WZ1 to predefined parameters for fixing screws on the doors. In machining zone BA2, for example, a boot lid is fitted with tool 1-2, WZ2, such that the control unit ST2 sets the machining tool 1-2, WZ2 to corresponding parameters. In automotive technology the length of the individual machining sections can be 6 m to 12 m, for example.
A fundamental problem of such a machining system SYS of the prior art can already be recognised from FIG. 2a. As the trailing cable installation 5-1, 5-2 likewise has to be suspended from trolleys in the rail 4, the entire cable harness has to be moved to and fro when operating the individual tool, which is very inconvenient for the operator. Moreover, if an additional machining tool is to be introduced, for example if machining section 2 is to be split into two further subsections, all the trolleys in the trailing cable installation and in the support mechanism have to be switched, which is extremely laborious. In some circumstances it is also necessary to reverse the left-right arrangement of tool and control unit, such that for this reason too the entire trailing cable along with the holding units 3-1, 3-2 may need to be removed from the roller rail 4. Furthermore, the limit switches, i.e. the out-of-range sensors 7-1 . . . 7-4 on the roller rail have to be set up again. In addition, each machining tool requires its own cable harness. Alternatively, if a flexible use of tools and a flexible changeover of tools is to be provided, a new rail would have to be set up in parallel, with new tools.
The addition of new tools or of new machining sections or machining zones is generally known as “rephasing” the assembly line. This is explained in more detail in FIG. 2. The entire assembly line is divided into a number of machining sections BA1 . . . BA6, whereby in each machining section a defined machining process is to be performed, for example screwing on the door, seat, window, bonnet, wheels, etc. Two or even more machining tools 1-1, 1-2 are typically provided for each machining section BA1 . . . BA6, which means that the arrangement in FIG. 2a may be found in every machining zone illustrated in FIG. 2b. 
If by way of example the sequence of steps BA1 . . . BA6 is to be changed, for example such that the bonnet is to be fitted before the window, the sequence for BA4 must be switched with BA3. This is known as rephasing the machining system SYS. As explained above, this requires the tool with its holding unit and the entire trailing cable to be switched, which is extremely laborious.
If a new phase is to be introduced, for example the fixing of a battery in machining step BA4′ between the fixing of the bonnet and the wheels in machining steps BA4, BA5, all the suspended cables must be shunted sideways or a new rail introduced in an additional phase. The out-of-range sensors also have to be set up again in turn. Rephasing and extending an assembly line is therefore extremely time-consuming and the trailing cable is inconvenient for the operator.